Eur. Phys. J. D 55, 637-643 (2009)
https://doi.org/10.1140/epjd/e2009-00248-8

Negative ion clusters in oxygen: collision cross sections and transport coefficients

¹ Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, P.O. Box 48, Mor., México
² Université de Toulouse, UMR CNRS 5213, UPS, 118 Route de Narbonne, 31062 Toulouse Cedex 9, France

Corresponding author: ^a jdu@fis.unam.mx

Received: 27 March 2009
Revised: 27 April 2009
Published online: 19 September 2009

Abstract

Using a pulsed Townsend experiment, we have observed the formation of two negative ion species in oxygen over the pressure range 100–600 torr, and the density-normalised electric field strength, E/N, from 2 to 14 Td. The peculiar shape of these transients has led us to propose a scheme of three-body ion-molecule reactions leading to the formation of O₄^- and O₆^-, which is substantiated by a curve fitting procedure. The resulting mobility data of these two ionic species have been used to calculate their respective momentum transfer collision cross sections, together with the dissociation cross sections that are needed to extend the range of calculation of mobility and diffusion (transverse and longitudinal) to 1000 Td. These calculations were based on an optimised Monte Carlo algorithm, using collision cross sections obtained from a JWKB approximation (Jeffreys-Wentzel-Kramers-Brillouin) or taken from literature.